The present invention relates to angel wing seals formed on the platforms of blades of a gas turbine rotor for sealing between the blades and nozzles and particularly relates to the profiles of the angel wing seals and methods of determining the profiles of the angel wing seals enabling a minimization of weight while maintaining seal stresses below a predetermined maximum or allowable stress.
Angel wing seals are axial extensions of a turbine rotor blade, i.e., a bucket, which form a seal by overlapping with nozzle seal lands forming part of the fixed component of a gas turbine. The angel wing seals inhibit ingestion of hot gases from the flowpath into gas turbine wheel spaces. Typically, angel wing seals are cast integrally as part of the blade or bucket. Conventional angel wing seals employ a linear profile in which the radially outer and inner surfaces of the seal form a wedge-shaped angle typically extending between the tip of the angel wing seals and fillets at the root of the seal with the blade platform. These linear profiles generate a stress distribution which is maximum at the root of the seal. Because dimensional designs are dictated by maximum stresses, extra material is necessary to ensure that maximum stress concentrations remain below an allowable stress level. There is a need, however, for angel wing seals which not only have stress concentrations at or below the maximum stress level but also which will provide a seal profile of minimum weight.
In accordance with a preferred embodiment of the present invention, there is provided angel wing seals and a method of determining the profile of angel wing seals which, for a given set of design parameters, identifies an angel wing section profile which minimizes the weight of the seals while maintaining the stresses in the seals below a maximum or allowable stress. Thus, for known design parameters and by iterative processes, maximum and allowable stresses, as well as the thickness along the length of the angel wing seal can be ascertained for those given parameters. Additionally, using further iterative processes, the profile of the radially inner and outer surface portions between the root fillets of the seal and the tip of the seal can be determined such that the angel wing seal weight is minimized while maintaining bending stresses at or below the maximum or allowable bending stress.
In a preferred embodiment according to the present invention, there is provided in a gas turbine having a rotor rotatable about an axis, blades carried by the rotor for rotation therewith and nozzles, a seal between each rotor blade and nozzles for inhibiting ingestion of hot gas from a hot gas flow through the turbine into turbine wheel spaces, comprising a seal body extending from a platform of the blade to a cantilevered tip thereof and generally axially toward lands on the nozzles, the seal body having radially outer and inner surfaces, each including a root fillet and surface portions between the fillet and the tip, one of the radially outer and inner surface portions extending non-linearly and disposed between the fillet and the tip.
In a further preferred embodiment according to the present invention, there is provided in a gas turbine having a rotor rotatable about an axis, blades carried by the rotor for rotation therewith, nozzles and seals between each rotor blade and the nozzles for inhibiting ingestion of hot gas from a hot gas flow path through the turbine into turbine wheel spaces, each seal having an upturn at a cantilevered tip thereof, a method of determining a profile of the seal, comprising the steps of for a given radial location of the seal relative to the rotor axis, material density of the seal, rotational velocity of the rotor, and thickness and width of the seal, determining a thickness profile along a length of the seal to maintain stresses along the seal below a predetermined allowable stress and to reduce the weight of the seal to a minimum.
In a further preferred embodiment according to the present invention, there is provided in a gas turbine having a rotor rotatable about an axis, blades carried by the rotor for rotation therewith, nozzles and seals between each rotor blade and the nozzles for inhibiting ingestion of hot gas from a hot gas flow path through the turbine into turbine wheel spaces, each seal having an upturn at a cantilevered tip thereof, a method of determining a profile of the seal, comprising the steps of, for a given radial location of the seal relative to said rotor axis, material density of the seal, rotational velocity of the rotor, and thickness and width of the seal, determining the maximum bending stress at selected locations along a length of the seal body and determining a thickness profile along a length of the seal body having minimum weight for the determined maximum bending stress or an allowable bending stress less than the maximum bending stress.
In a further preferred embodiment according to the present invention, there is provided in a gas turbine having a rotor rotatable about an axis, blades carried by the rotor for rotation therewith, nozzles and seals between each rotor blade and the nozzles for inhibiting ingestion of hot gas from a hot gas flow path through the turbine into turbine wheel spaces, each seal having an upturn at a cantilevered tip thereof, a method of determining a profile of the seal, comprising the steps of, for a given radial location of the seal relative to the rotor axis, material density of the seal, rotational velocity of the rotor, and thickness and width of the seal, determining the maximum bending stress Smax at selective locations along a length of the seal conforming to the equation       S    max    =                    6        ⁢                  z          0                ⁢                  xe2x80x83                ⁢        ρ        ⁢                  xe2x80x83                ⁢                  ω          2                                      h          2                ⁢                  xe2x80x83                ⁢                  (          x          )                      ⁡          [                        ab          ⁢                      xe2x80x83                    ⁢                      (                          x              -                              a                2                                      )                          +                              ∫            0            x                    ⁢                      h            ⁢                          xe2x80x83                        ⁢                          (              ξ              )                        ⁢                          xe2x80x83                        ⁢                          (                              x                -                ξ                            )                        ⁢                          xe2x80x83                        ⁢                          ⅆ              ξ                                          ]      
wherein the mass of the seal is determined by       M    a    =      ρ    ⁢          xe2x80x83        ⁢    W    ⁢          xe2x80x83        ⁢          (              ab        +                              ∫            0            L                    ⁢                      h            ⁢                          xe2x80x83                        ⁢                          (              x              )                        ⁢                          xe2x80x83                        ⁢                          ⅆ              x                                          )      
and wherein Z0 is the radial location of the seal body centerline relative to the axis of rotation of the rotor, xcfx89 is the angular velocity of the rotor, xcfx81 is the density of material forming the seal body, a is the width of the upturn, b is the height of the upturn and x is the distance from a tip of the seal in a direction parallel to the rotor axis to a location measured from the tip.